Women are at a lower risk than men for cardiovascular disease, including stroke, yet cerebral ischemic events do occur in both sexes at all ages. The vasoactive hormone, estrogen, has historically been considered to be protective in coronary heart disease, but it is not clear if the steroid is also an important neuroprotectant in either women or men. Most critically, the comparative vulnerability of females and males to tissue once stroke is ongoing remains unknown. Our preliminary findings with focal cerebral ischemia in animals, as well as previous data with global reduction of cerebral blood flow, clearly suggest that females have better outcomes after stroke than males and that ischemic events can be altered by estrogen-priming of the cerebral vasculature and of brain. While protection conferred by estrogen is biologically feasible, specific neuroprotective mechanisms are unknown and potentially include both vascular and neuronal actions the overall purpose of this study is to determine if there are inherent sex-linked injury mechanisms in salvaging brain tissue after an ischemic event. In Aim 1, we will determine if histopathological and neurobehavioral outcomes after focal ischemia (middle cerebral artery occlusion, MCAO) are more favorable in female versus male rats and if endogenous estrogen is the source of neuroprotection. In Aim 2, we will examine if endogenous and exogenous estrogen alter ischemic outcomes by a vascular mechanism, focusing on a estrogen receptor-protein kinase G mediated signaling pathway with subsequent activation of vascular smooth muscle calcium dependent K channels. The third aim will determine if injury from MCAO is exacerbated in transgenic mice deficient in estrogen receptors (estrogen receptor knock-outs). In Aim 4, we examine a neuronal mechanism, hypothesizing that estrogen reduces ischemic neuronal injury by a bcl-2 mediated mechanism which is dependent on nuclear estrogen receptors. The proposed study will contribute to our understanding of cerebrovascular disease in females and the role of estrogen as a potential neuroprotective therapy for patients of either sex.